The power transmission of this invention is a phase controller having an input shaft and an output shaft which is interposed between two rotating elements. The present invention provides the ability to continuously and dynamically adjust the relative phases between the input and output shafts without altering the relative speeds of the rotating components.
Phase controllers are commonly utilized in timing applications between two or more rotating machine components. For instance, phase controllers are used to advance or retard the timing of feeders, index heads, registration systems, marking and printing heads, glue and label applicators and timing screws. Phase controllers are also used to coordinate the timing of cut-off knives, feed rollers, conveyors, transfer mechanisms, packaging machine components, and die cutting and cut-off heads. Phase control is necessary any time the relative rotation of two or more elements must be regulated or coordinated with respect to each other.
For the purposes of this application, it should be noted that phase control does not attempt to alter the speed of rotation of the distinct rotating elements. Rather, phase control as used in this application, is intended to alter the angular position of distinct points on each of the rotating workpieces.
Commonly, phase controllers or phasing transmissions incorporate a gear cage rotatably mounted about the input shaft and output shaft of the transmission to control the relative phases of the two shafts. Such a phasing transmission is disclosed in U.S. Pat. No. 3,565,104 wherein a pair of opposed spider gears are engaged between the pinon gears and the input shaft and the output shaft of the transmission. The spider gears are carried by a ring gear which rotates about 360.degree., thereby moving the position of the spider gears with respect to the pinion gears to adjust or alter the relative phases of the input shaft and output shaft. The phase controller described in U.S. Pat. No. 3,565,104 uses a manual adjustment screw to impart rotation to the ring gear, thus varying the phases of the input shaft and the output shaft of the transmission. Rotation of the ring gear can also be achieved through the use of a motor control placed on the adjustment screw. Such motors are usually mounted in a location outside of the housing of the phase controller transmission.
Phase controllers such as the device disclosed in the U.S. Pat. No. 3,565,104 suffer from problems inherently found in most devices which utilize a series of intermeshed gears. Perhaps the most exasperating problem is the existence of backlash due to the engagement between the series of intermeshed gears and there is ongoing interest in providing a simple and low cost solution to the problems of backlash in phase controller transmissions.
Recently, somewhat improved backlash characteristics have resulted from the introduction of harmonic drive devices, utilizing strain wave gearing, into the structure of phasing transmissions. Phasing transmissions having a harmonic drive component have enhanced the ability to accurately control the relative phases of two rotating elements while reducing the potential for backlash when compared to phase control devices such as that shown in U.S. Pat. No. 3,565,104. Such harmonic drive devices generally consist of a pair of circular internal gears, the dynamic spline and the circular spline. The circular spline carries more teeth than the dynamic spline; in most common designs, two more teeth. A third member, the flex spline, is an external gear of an outside diameter slightly less than the inside diameter of the two internal gears and is designed to flex to engage the internal gear teeth of the dynamic spline and circular splines. Generally, the flex spline comprises a thin walled steel ring with the same number of external spline teeth as the dynamic spline. The flex spline is of a diameter, that when placed inside the dynamic spline and the circular spline, will not universally engage the gear teeth of the dynamic spline and circular spline about 360.degree.. In fact, the flex spline will only engage the gear teeth of the circular and dynamic splines when pressed into an elliptical shape having a major axis and a minor axis. The gearing teeth will engage about the major axis and will not engage at all on the minor axis.
The dynamic input to such a harmonic drive device is usually provided by a wave generator which has an elliptical bearing and a rotating input element. The rotating elliptical shape of the wave generator imparts a rotating elliptical shape to the flex spline causing the exterior gearing of the flex spline to engage the interior gearing of the dynamic spline and the circular spline in a progressive nature about the axis of the harmonic drive device. As the flex spline progressively rotates about its engagement with the circular spline and dynamic spline the differential in teeth between the dynamic spline and the circular spline will establish a phase change between the dynamic spline and the circular spline equal to the tooth differential for every one revolution.
In most designs where a harmonic drive device is utilized with a phase controller transmission, it is positioned between the input shaft and output shaft of the transmission. Many times the input shaft of the transmission has a hollow core extending therethrough along its axis. Thus, a control motor placed on the exterior of the transmission is usually engaged, via a driveshaft inserted through the hollow core of the input shaft, with the wave generator of the harmonic drive device. The exterior mounted motor can then control the harmonic drive device thereby controlling the relative phases of the input shaft and output shaft of the phasing transmission.
It has been found that such a use of a harmonic drive unit incorporated into a phase controller transmission has succeeded in reducing the potential for backlash in the phase controller transmission to about 20 minutes or one-third of a degree. However, the physical arrangement of the drive components for this type of harmonic drive phasing transmission presents problems when the phasing transmission must be placed in areas having limited space availability. Further, for many applications, 20 minutes of backlash remains an unacceptably high amount of backlash and is therefore undesirable.
Therefore, it is an object of this invention to provide a phase control transmission having self-contained components for the purposes of meeting design and space constriction requirements.
Another object of this invention is to provide a phasing control transmission which is infinitely adjustable about 360.degree. and can be accurately and consistently controlled.
Yet another object of the present invention is to provide a phasing control transmission having backlash potential approaching zero.
These objects are met by the improved phase controller transmission of the present invention. The present invention provides for an improved phase controller transmission which solves the problems of incorporating a harmonic drive member into the design of the phase controller transmission and facilitates the further reduction of backlash potential to practically zero.